1. Field of the Invention
This invention relates to new and useful improvements in diamond drill bits in which the bit body or a bit component, such as a cutting blade, has a carbide coated exterior surface and more particularly to methods of producing such bit bodies and bit components.
2. Brief Description of the Prior Art
Rotary drill bits used in earth drilling are primarily of two major types. One major type of drill bit is the roller cone bit having three legs depending from a bit body which support three roller cones carrying tungsten carbide teeth for cutting rock and other earth formations. Another major type of rotary drill bit is the diamond bit which has fixed teeth of industrial diamonds supported on the drill body or on metallic or carbide studs or slugs anchored in the drill body.
There are several types of diamond bits known to the drilling industry. In one type, the diamonds are a very small size and randomly distributed in a supporting matrix. Another type contains diamonds of a larger size positioned on the surface of a drill shank in a predetermined pattern Still another type involves the use of a cutter formed of a polycrystalline diamond supported on a sintered carbide support.
Some of the most recent publications dealing with diamond bits of advanced design, relevant to this invention, consists of Rowley, et al. U.S. Pat. No. 4,073,354 and Rohde, et al. U.S. Pat. No. 4,098,363. An example of cutting inserts using polycrystalline diamond cutters and an illustration of a drill bit using such cutters, is found in Daniels, et al. U.S. Pat. No. 4,156,329.
The most comprehensive treatment of this subject in the literature is probably the chapter entitled Stratapax bits, pages 541-591 in Advanced Drilling Techniques, by William C. Maurer, The Petroleum Publishing Company, 1421 South Sheridan Road, P.O. Box 1260, Tulsa, Okla., 74101, published in 1980. This reference illustrates and discusses in detail the development of the Stratapax diamond cutting elements by General Electric and gives several examples of commercial drill bits and prototypes using such cutting elements.
The hardfacing of roller bit bodies with tungsten carbide has been known for many years. Tungsten carbide hardfacing has been applied to the bit body prior to final assembly. Conventional hardfacing techniques, however, require the use of sufficiently high temperatures for application of the tungsten carbide coatings that the metallurgical properties of the steel body may be adversely affected. Attempts have been made to apply tungsten carbide coatings to bit bodies by conventional plasma spraying systems and by explosive-type coating methods. Such systems produce only very thin coatings and either do not adhere to the steel surface adequately or are too thin to withstand the severe conditions encountered in earth drilling.
Hardfacing of drilling tools, including tool joints, drill collars and rotary cone bits is found several places in the patent literature and summary of the art as of about 1970 is given in History of Oil Well Drilling, J. E. Brantly, Gulf Publishing Co., 1971, pp. 1028, 1029, 1081.
The patent literature includes a number of instances of tungsten carbide components being molded into a finished object.
Baum U.S. Pat. No. 4,146,080 discloses a composite material consisting of a refractory metallic carbide particles in a local matrix alloy having a lower melting point in the carbides. These composites are prepared by placing sections of refractory metallic carbide, at least some of which are larger in size than those desired in the final composite, in a mold. Matrixing alloy is heated above the melting temperature of the binder metal employed in this sintered carbide and then poured into the relatively cold mold. The binder metal dissolves and leaves the outer surfaces of the sections and diffuses into the alloy which is allowed to cool naturally and solidify. The final composite contains micron size particles of the carbides that are released from the large section when the binder melts.
Baum U.S. Pat. No. 4,024,902 discloses composites consisting of sintered tungsten carbide particles in a matrix of a steel alloy having carbon, cobalt and tungsten content which are prepared by placing particles of tungsten carbide with cobalt binder, at least some of which are larger in size than those desired in the final composite in a mold. Matrixing alloy having little or no tungsten content is heated above its melting temperature and then poured into the relatively cold mold. The carbon, tungsten and cobalt dissolve at the outer surfaces of the particles and diffuse into the alloy which is allowed to cool naturally and solidify.
The Baum patents disclose the use of the described process in the preparation of composite articles, including coated articles, containing tungsten carbide, or other refractory hard metal, for hardness and abrasive wear.
Bridwell U.S. Pat. No. 3,175,260 discloses the preparation of a composite casting by casting a matrix metal into a mold having carbide particles packed along two sides of the mold to provide a shaped metal body coated with the refractory carbide. The process is described as being useful for refractory hard metals in general, including tungsten carbide, titanium carbide, tantalum carbide, niobium carbide, etc. Binder metals include the iron group metals.
Bidwell U.S. Pat. No. 3,145,790 discloses the formation of refractory metal carbide coatings in the form of a layer on drag bits and also on the bit bodies of a drag bit.
Bidwell U.S. Pat. No. 3,120,286 discloses another drag bit having hard facing formed thereon.
Krussel U.S. Pat. No. 1,939,991 discloses a diamond cutting tool in which the tool body is of a sintered refractory carbide or other hard metal.
Heinkel U.S. Pat. No. 1,043,831 discloses casting a cutting wheel with metal cutters being provided in the form of inserts secured in the mold. The inserts are incorporated into the cutting wheel.
Cottrell U.S. Pat. No. 2,184,776 discloses the casting of a bit body around hard metal, i.e. refractory carbide cutting inserts.
Eklund U.S. Pat. No. 2,743,495 discloses production of a composite cutter in which a bit body is molded or cast around carbide inserts.
Koebel U.S. Pat. No. 2,200,281 discloses molding cutters of sintered hard metal as supports for diamond cutting elements.
Wittlinger U.S. Pat. No. 2,260,593 discloses molding sheets of carbide material onto the surface of cast tooth pipe cutter.
The prior art teaches the use of tungsten carbide and other sintered refractory hard metal coatings for hardening and protection against abrasive wear in various types of tools including various drill bits. Prior art such as Bidwell U.S. Pat. No. 3,175,260 and Baum U.S. Pat. Nos. 4,024,092 and 4,146,080 disclose the desirability of molding composite objects, including bit bodies, having wear resistant refractory carbide surfaces.
Drill bits using diamond type cutters supported on steel bit bodies cannot utilize the technique of casting the bit body with a refractory carbide coating in place because the temperature of the mold metal is considerably higher than can be tolerated by the diamond cutting inserts. Some efforts have been made to provide refractory carbide or other hard metal coatings on bit bodies for diamond type cutters by use of various hard facing techniques and these processes have been thoroughly unsatisfactory in that the temperature of the diamond cutters is raised above the point at which the cutters are damaged. There has been a substantial need for a diamond drill bit having the surface of the bit body completely coated with a refractory hard metal such as sintered tungsten carbide. The refractory hard metal, e.g. tungsten carbide, coating cannot be applied over the entire surface of the bit body at the time the bit body is cast since the hard coating makes it virtually impossible to drill the bit body for addition of the cutting elements, wear pads, and other drill bit components. Consequently, the need for a diamond drill bit having the surface of the bit body completely coated with tungsten carbide or other refractory hard metal continues and has not been solved by the prior art.